Actuator



Aug. 15, 1961 R. D. ATCHLEY ACTUATOR 2 Sheets-Sheet 2 Filed May 23, 1960Y ,5 j f/v 7b4/w, w @i d 0 6 2% L6 6 67 n@ .y W IIIIVU'IIIHHII.: .1Ef... L] 9 w 7 7 f I w w ,w w M a @w l f7 5 f3 1 d A# United StatesPatent G 2,996,072 ACTUATOR Raymond D. Atchley, Los Angeles, Calif.,assigner, by mesne assignments, to American Brake Shoe Company, NewYork, N.Y., a corporation of Delaware Filed May 23, 1960, Ser. No.39,914 19 Claims. (Cl. 137-83) This application is a continuation-impartof application Serial No. 755,534, filed August 18, 1958, and Serial No.755,775, filed August 18, 1958, now Patent Number 2,962,611, each ofwhich is in turn a continuation-in-part of Serial No. 681,310, filedAugust 30, 1957, now Patent No. 2,884,907.

This invention relates to improvements in actuators.

IIt is an object of the present invention to provide a novel actuatordesign whereby a small change in signal input produces 'a large changein the unit controlled by the actuator.

Another object is the provision of an actuator comprising a movable beamor an armature and a motion transmitting device connected thereto, sucharmature and device being designed to be responsive to a small change insignal input.

A further object of the invention is the provision of an actuator inIwhich the signal is mechanically applied to an armature in terms of anapplied force or pressure tending to produce rotation of the armature.

-A still further object is the provision of an actuator in which fluidpressure responsive devices are mechanically connected to the armatureand wherein a small effective pressure causes actuation of the armature,or alternatively, a large displacement of the armature can be producedfor any given effective pressure applied against the armature.

The actuator of my invention is designed to have a low stiffnesscoefficient yand thus have a low natural frequency and to contain amovable member which is responsive to signals of low force and to have arelatively large displacement for low values 'of applied signal force.

The signal applied is in the preferred embodiment a mechanical force asdistinguished from one applied by means of an electromagnetictransducer.

-In my preferred embodiment the force is applied to the movable membereither hydraulically or pneumatically.

The system for -application of force to the movable member creates abalance of moments, each of large value but resulting in net moments oflow value to cause the displacement of the movable member.

The actuator of the invention comprises basically a yieldably suspendedarmature mounted ladjacent the pole pieces of permanent magnet means. lnpreferred practice the armature is suspended on a flexural constraint orilexure member. Means are provided for deflecting the armature byapplication of a force to said `armature corresponding to the magnitudeof a signal received by the force applying means. Unlike the actuator ofmy copending applicatiom the force is a mechanical force and does not ofitself modify the flux of the permanent magnets. A motion transmittingdevice, e.g. in the nature of a rod or jet pipe, as described mo-refully below, is connected to the armature for movement in response todisplacement of the armature on the yieldable constraint or ilexure.lSuch rod or jet pipe transmits the motion of said armature in responseto said signal to a unit such as a hydraulic motor which is beingcontrolled by the actuator.

The armature is constructed of a magnetically permeable material, and asthe armature is displaced from its initial position toward a magnet polepiece, a greater attractive force exists between the armature and theRCC pole piece of the permanent magnet means toward which it is beingdisplaced. This attractive force is in a direction opposite to therestoring force of the stressed yieldable constraint or flexure on whichthe armature is mounted. This effectively reduces the restoring force.The displacement obtained by the application of the signal force is thusgreater than would be obtained in the absence of the magnets. Thecoefficient (spring constant) which relates force to displacement isthus reduced, that is the stiffness of the device is thus effectivelyless. The mechanical stiffness is considered a positive stiffness orspring constant and for like reason the effect of the magnetic force isconsidered to `introduce a negative stiffness or spring constant.lldeally if the negative magnetic stiffness balances the mechanicalstiffness there is ideally no restoring force exerted by the yieldableconstraint to oppose the signal force causing displacement of thearmature, and a minute signal force applied against the armature willproduce a relatively large displacement thereof, and at zero stiffnessan infinitely large response from the actuator control, that is, the,rod, jet pipe 'or other linkage connected to the armatufe, o'r arelatively large displacement of the armature is obtained `for a givenapplied force. As la practical matter the stiffnesses are n'ot exactlyin balance and the net stiffness may be either positive or negativedepending on' the system into which the actuator is embodied. p v

The armature restoring force is large and ideally substantially producedby any means applying la force independent of the system stiffness andwhich opposes the signal force in magnitude and direction to restore andmaintain the system in a null or balanced condition. 'Such restoringforce can be produced, for example, by a feedback to the armature andmay come either directly as a result of the motion of the armature orfrom some device actuated by the motion of the armature. This feedbackconnection introduces a degeneration of the signal force and acts as arestoring force to null out the motion of the armature. An example ofsuch feedback is described in my above copending applications.

The attractive force between the armature and the pole piece towardswhich it moves varies as the square of the distance between the armatureand such pole piece'. The negative force or the mechanical stiffness ofthe )deldable constraint is substantially constant. Thus, the ratiobctween the mechanical stiffness of the yieldable constraint and themagnetic stiffness is variable. However, for small displacement of thearmature, e.g. less than about one third the distance between thearmature in its centered position and the adjacent pole piece, themagnetic stiffness provided by the pole pieces of the permanent magnetmay be considered substantially constant because of the nature of thesquare law effect on the magneticstiffness.

Because of the feedback provided, the system of the invention isdesigned to operate as a null balance unfit so that the displacement ofthe armature is very minute, and under such operating conditions theratio of the mechanical stiffness of the flexible constraint to themagnetic stiffness is substantially constant. Due to' the greatreduction in stiffness of the system, a greater response is obtained fora given frequency of movement of the armature as compared to prior artsystems. In employing the actuator described here with Ithe servomechanism described in my copending applications and previous patent, alarge gain from the hydraulic amplier is obtained. By permittingdisplacement of the armature by a small force, a greater dynamicresponse is obtained. e .A

The means for applying a force to the armature responsive to a signalreceived by such means,- can be any mechanical force applying means,such as a rod, diaphragm, bellows or the like. As a feature of theinventiom a plurality of such force applying means are employed in' anarrangement such that forces of large magnitude applied to the armatureare resolved into a net ditferential force of small magnitude. Means mayalso be provided for setting the armature in its null positioncorresponding to a predetermined reference force applied to thearmature.

According to one embodiment of :the invention a plurality of tiuidpressure diaphragms or bellows are attached mechanically to the armaturewhich is mounted for angular motion about a pivot or hinges. One or moreof such bellows may be actuating bellows to which the iiuid pressurebeing sensed or measured is conducted, while one or more bellows may besubjected to a constant pressure. The various bellows are positionedwith respect to the pivot point of the armature so that a minutedifferential pressure resulting from the signal applied to the actuatingbellows produces a moment tending to displace the armature angularly.

Instead of employing a plurality of bellows a single bellows can beconnected to the armature to function as the force applying meansresponsive to the input signal.

The invention will be more readily understood by reference to thedescription below of a predeferred embodiment, taken in connection withthe accompanying drawing wherein:

FIG. 1 is a section in elevation, through the invention actuator;

FIG. 2 is a section taken on line 2-2 of FIG. 1;

FIG. 3 is a perspective view of the torsional flexure for the armatureof FIG. 1; and

FIG. 4 is a section taken on line 4-4 of FIG. 1.

Referring to the drawing, the valve case 1 is provided with an axialbore 2' therein. Case 1 also has a hole 2 (see FIG. 4) which intersectsaxial bore 2'. Additional bores such as 3 and 4 are also provided incase 1. Bores 3 and 4 may be connected to a reversible hydraulic orpneumatic motor (not shown) being controlled by the actuator hereindescribed. Positioned in bore 2 is a sleeve 5 which is retained in case1 by retaining nuts 6. The case 1 and bore 7 of sleeve 5 are sealed bytwo end caps 8 held in place by suitable bolts 9. Sleeve 5 is grooved ata plurality of locations 10 to give a series of lands 11, which aresealed by O-rings 12, and the sleeve 5 is ported with bores 13.

'I'he sleeve 5 ca rries a spool 14 in the form of a piston which makes asliding engagement with the interior of sleeve 5 by means of lands 15,forming bores such as 16 intermediate the lands. Positioned at each endof bore l'7 are stop members 17 sealed by O-rings 18. The sleeve isfurther formed with bores at 19 into which the cone tip receptor jets 20and 21 each provided with an inclined bore, 20 and 21', are pressed. Thebore of jet 20 communicates via cross bore 22 with a port 22, and thebore of jet 21 communicates via cross bore 23 with a port 24, ports 22and 24 connecting with chambers 25 and 26 in sleeve 5, adjacent theopposite ends of spool 14.

Positioned in the spool piston is a feedback spring held in the spool bymeans of a set screw 28 inserted through the threaded bore 29.

The structure described above and its function are more fully describedin my Patent No. 2,884,907, and such description in said patent ishereby incorporated into this specilication by reference.

Carried on the upper face of the case 1 is an assembly, indicatedgenerally by numeral 49, which is mounted on a mounting base 50 and iscomposed of a frame 52 which carries the armature 56 mounted on torsionmembers 55 (see FIGS. 3 and 4) formed by milling the shaft member 54 toform a thin spring web member. One end of the shaft S4 is rigidly xed toframe 52 by brazing, and the other end is formed as a fork 54' intowhich the armature 56 is rigidly fixed by brazing. At each end of theframe 52 is positioned a pole and magnet assembly composed of a C-shapedmagnet 57 and a C-shaped magnet 57 oriented with their north poles andsouth poles opposite each other, each such assembly carrying a polepiece 58 at the north pole and a pole piece 59 at the south pole spacedfrom each other to produce a gap 58'. The armature 56 is positionedsymmetrically in each of said gaps to give four equal gaps, two at oneend of the armature and two at the other end between the adjacent polepieces. Interiorly of the frame 52 and abutting the pole pieces 58, oneat the north pole and one at the south pole, are the magneticallyconductive members or pieces 60.

The frame 52 is bored at 63 and the bars 60 are bored at 60 and thearmature is bored at 65 to receive the jet pipe 64 which is positionedwithin the bores 63, 60' and 6'5, pipe 64 being rigidly affixed to thearmature 56 in the bore 65. The iiexible pipe 66, axially aligned withthe pipe 64, is rigidly connected to the armature 56 in a counterbore66. The mounting 50 of the torque motor is bored at 50' to permit thepassage of the tube 66 and the pipe 64. The tube 66 is rigidly connectedat its end 66" to the fitting 50. The fitting 50 is connected to the topof the case 1 and sealed by means of O-rings 50a as shown.

The pipe 64 has an ejector jet 65 brazed to it and extends into 4theslot 42 and is connected at its lower end to the .feedback spring 27 atthe slot 42. The pipe 64 is bored with an axial bore 68, which connectswith a cross bore 7i and a sufficiently flexible pipe 72 (see FIG. 4).The pipe 72 registers and is in liuid communication with the bore 73which communicates with the bore 1 via restricted orifice 74 and thefittings 74 and 74 between which is positioned the screen 74a, asdescribed more fully in Patent No. 2,884,907.

The receptor jets 20 and 21 are pressed into the sleeve 5 so that theangularly disposed bores 20' and 21' of the jets are so positioned thatthe center line of the bore 68 bisects the acute angle between the axisof the bores 20 and 21. The ends of the nozzles 20 and 21 aresymmetrically positioned with respect to the center line of bore 68.

A iirst fluid pressure bellows 75 is connected between upper bar 6l) onframe 52 and one side of the upper face of the armature 56, and a secondfluid pressure bellows 76 is connected betwen such bar 60 and the otherside of the upper face of the armature 56. The axis of each of `thesebellows is positioned equidistant from the axis of rotation of thearmature 56. A third fluid pressure bellows 77 is connected between thelower bar 60 on frame 52 and the lower face of one side of armature S6,and a fourth fluid pressure bellows 78 is connected between the lowerbar 60 and the lower face of the other side of the armature. The axis ofeach of the bellows 77 and 78 is positioned equidistant from the axis ofrotation of the armature 56. However, it will be noted that the axis ofeach of the lower bellows 77 and 78 are each displaced an equal distancefrom the axis of rotation of the armature, somewhat greater than thedistance of the axis of each of the upper bellows 75 and 76 from suchaxis of rotation. Fluid pressure inlets 79 and 79 are provided for uidcommunication with the interior of bellows 75 and 76, respectively.Fluid communication between bellows 7S and 77 and between bellows 76 and78 is provided by the respective channels 86. Thus, the pressure inbellows 77 is the same as that ap plied to 75, and the pressure inbellows 78 is the same as the pressure applied to belows 76.

One end of the armature 56 has mounted thereon by means of screws 81 ayoke 80. A spring 82 has its upper end connected to the upper crossmember 83 of the yoke, the other terminus of the spring being connectedto an adjusting screw 84 threadably engaged in the upper face of case 1.By adjusting screw 84 the initial position of the armature between thepole faces of magnets 57 and 57 can be set as desired. Thus, forexample, if the initial pressures applied to the bellows, as describedmore fully below, cause a clockwise rotation of armature 56, viewingFIG. 1, screw 84 is turned down sufficiently to center the armaturebetween the pole pieces, and if there is a tendency towardcounterclockwise rotation ofthe armature -due `to the initial -forcesapplied by the bellows, the screwp84 is backed off suciently to raisethe arma- `ture to a centered position. During adjustment of screw "84,the cover 90, which normally encloses theassembly y49,is removed andafter adjustment of screw 84, the

cover is'replaced and attached to the case 1 by means of screws 91.

The interconnected bellows 76 and 78, and/or the `interconnected bellows75 and 77 may be subjected to a positive pressure, atmospheric pressure,or a vacuum. A

Vreference pressure, which may be a positive absolute `zero level of thesignal which is to be employed may be applied to bellows 75 and 77. Atthis base pressure corresponding to zero signal level the hydraulic orpneumatic motor being controlled by the actuator through ow of liluidvia bores 3 and 4, is in the desired operating position. As result ofthe oiset position of bellows 75 and 77, a clockwise moment will beexerted by bellows 77 `against armature 56, as result of the base levelpressure applied in bellows 75 and 77. Since such clockwise moment willbe of greater magnitude than the opposing counterclockwise momentproduced by the lower reference pressure in bellows 76 and 78, therewill be a resulting net clockwise moment exerted against the armature.l1`his will cause the jet pipe 64 to pivot to the left, viewing FIG. 1,causing a greater pressure in the receptor jet 20 than in the receptorjet 2d, thus producing a greater pressure in chamber 25 than in chamber26, and resulting in a displacement of the spool 14 to the right. Thiswill result in a valving of the iluid by the spool to cause a ow of Huidthrough the valve to the tluid motor controlled by the spool valve.

In order to center the armature 56 to return the spool 14 to the nullposition shown in FG. l, the adjusting nut 84 is turned down to rotatearmature 56 counterclockwise against the net clockwise moment applied bybellows 77 until the armature and the jet pipe are centered. Since nowthe moment on the armature produced by the signal force is balanced bythe spring 82, the tension in the Vfeedback spring moves the spool backto its central null position. This adjustment of screw 84 andcounterclockwise rotation of armature 56 rotates the pipe 64 back to itscentered position shown in FlG. l, with respect to receptor jets 2t) and21. This equalizes the ilow of fluid in bores 26" and 2li `of thereceptor jets and equalizes the pressure applied against the ends ofspool` 14. The centering of pipe 64 and the armature S6 and thebalancing Vof the signal force by the spring SZ returns the spool 14 toits central position, as shown in FIG. 1. This will be indicated by acessation `of ow of fluid from ports 3 and 4 to the hydraulic motor.rl'he armature 56 is now in a centered position with the oppositelyapplied moments of bellows 77 and 78 balanced, and the hydraulic motorbeing actuated is in the correct operating position desired for a netsignal force at the design level of zero signal pressure.

Assume that no signal is impressed on the bellows 75 and 77,so that thearmature 56 is in the null position and centered in [the gaps betweenthe pole pieces 58 and 59, as shown in FIG. 1. The jet pipe 64 isundeected and the tube 66 is unbent and aligned symmetricallyV over 21'symmetrically placed, each of such bores will receive au equal amount offluid from the jet'65. The'lluid 6 through 20 and 21 being thus underequal pressure exerts equal Ypressure against the opposite ends ofspool'i1'4, and the spool 14 is centered,`as'shown in FIG. '1. The'sp'oo'l 14 is thus hydraulically balanced, notwithstanding `flow Vofiluid yin jet pipe 64V and through receptor ,jets Z0v and 21, and thehydraulic motor is not actuated.'

If, new, the signal `generated .from the hydraulic or other motor beingcontrolled by the actuator produces a pressure in bellows 75 and 77ygreater than the initially set pressure therein, a relatively smallydifferential clockwise moment is-Iintroduced against the armature '56yby bellows '77, tending to produce clockwise rotation of armature 56.The pipe 64 will rotate clockwise to the left as viewed in RIG. 1,producing a greater flow of duid in bore Z0' than 21 of the receptorjets and a displacement of the spool 14 to the right. This displacementof spool 14 causes a flow of Huid from the actuator via ports 3 and `4to the hydraulic motor being controlled, to displace the hydraulic motoror to actuate it.

It `will be observed that as the spool is displaced to the right,viewing FIG. l, a spring force is imposed upon the pipe 64 by means 'ofthespring 27, which spring force is Yproportional to the displacement ofthe piston spool so that the spring introduces a restoring Yforce in anamount equal to balance Vthe force causing movement of the armature inresponse to the signal, and to restore the pipe 64 to its neutralposition, shown in FIG. 1, -at

which place the pressure in nozzles Z0 and 241 and chambers 25 and 26are again equal, and further displacement of the piston cannot occur.The spring 27 thus acts as a force feedback to null out and balance theforce of the signal causing the initial displacement. It will be observed that in so doing the initial displacement of the piston occurringupon the reception of the signal is not altered so lon-g as the signalforce applied to the actuator is at the original strength and direction.In consequence thereof, upon the reception of a signal by the armaturethe ejector jet pipe 64 is disp-laced an amount proportional to theforce of the signal in Ia Idirection determined by the direction of thesignal, and the piston spool is displaced an amount proportional to thesignal strength in a direction determined by the direction of thesignal, and is maintained in such displaced condition so long as thesignal remains unchanged in Imagnitude and direction. Should the signalfall in strength but not reverse in direction, the spring force at Z7will move the jet pipe 64 to the right, viewing FIG. l, and now the bore21 receives more uid than does the bore 20, and the pressure in chamber2.6 is greater than in chamber 245, and the spool 14 moves to the left.However, in so moving, the tension in the spring Z7 will move the jet65' to the left to relax the tensi-'on to a value proportional to thenew spool position closer to the center position, and reducing the flowof fluid exiting through 3 to the hydraulic motor and returning through4. This may continue until the signal strength falls to zero, in whichcase the spool is centered and no fluid flow occurs in the hydraulicmotor.

The function of the force feedback spring is described in greater detailin my Patent 2,884,907, and such disclosure in incorporated herein byreference.

Substantially the same mode of operation except in reverse to thatdescribed above takes place when the signal from the hydraulic motorbeing controlled by the actuator is reversed in direction, producing apressure in bellows 75 and 77 less than the pressure at the set zerosignal level, but in this situation the small net moment produced asresult of the longer moment arm of bellows 7S as compared to bellows 76will produce a counterclockwise motion of armature 56 and jet pipe 464,and a displacement of spool 14 to the left. This will result in areversal of ow of fluid to the hydraulic motor.

It will be noted particularly that very large pressures can beintroduced into the bellows 75 'and 77, but due ,.7 to the slightlyoiset relation of bellows 77 with respect to bellows 7S, and of bellows78 with respect to bellows 76, the net moment produced against armature56 by the pressure in bellows 77 is very small, and hence the actuatorof the invention can be made very small, yet is able to handle largesignal pressures. Further, due to the balancing out of the mechanicalstiffness of the ilexure 55 by the magnetic attraction of the magnets 57and 57' for the armature 56, so that there exists substantially norestoring force exerted by the flexure SS to oppose the pressure, e.g.in bellows 77, causing a displacement of the armature, Weak exures canbe used. In such case the natural frequency may be made low, and bysuitable selection of magnets and thus the magnitude of the magneticstiffness, this frequency may be adjusted up to the natural frequency ofthe system.

It is further to be noted that by means of the instant device, while theoperation of the actuator has been described in terms of an actualrotation of the armature by the forces imposed thereon, there isactually practically no displacement of the armature, but rather only atendency toward displacement, as result of changes in pressure inbellows 75 and 77 produced by changes in the input signal. The actuatorhereof has as an additional advantage improved response at a givenfrequency.

Instead of employing a bellows system, any other mechanical means can beemployed for impressing the signal on the armature from the device beingcontrolled.

Instead of applying the invention actuator in conjunction with a servomechanism of the type described in my above Patent 2,884,907, I mayeliminate the jet pipe and spool valve structure described herein andconnect the armature by suitable linking mechanism for control of anydesired device. Thus, for example, I may employ my actuator,substituting, for example, a rod in place of the jet pipe 64, andeliminating the spool valve structure described herein, for controllingany other desired mechanism, by displacement of such rod, such as thesystem described in my application Serial No. 755,775, or by connectinga rod in the place of a jet pipe, the device may be used as a transducerto cause a displacement of a force summing means responsive to apressure, e.g. as a pressure gage.

Although I have shown a Iforce feedback connection between the spool andjet pipe, I can instead employ a position feedback in the nature of arigid connection between the jet pipe and spool.

Also, it will be understood that I can substitute any other suitablepermanent magnet device for the specific permanent magnet systemdescribed above.

While I have described particular embodiments of my invention for thepurpose of illustration, it should be understood that variousmodifications and adaptations thereof may be made within the spirit ofthe invention as set 4forth in the appended claims.

I claim:

1. An actuator which comprises an armature composed of magneticallypermeable material, a yieldable mounting for said armature, permanentmagnet means positioned in operative relation adjacent said armature,means for mechanically applying a force to said armature in response toa signal, to move said armature from a null position, the force ofmagnetic attraction of said permanent magnet means substantiallybalancing the mechanical stiffness of said yieldable mounting, and amotion transmitting device connected to said armature and operative inresponse to motion of said armature, and means for applying to saidarmature a restoring force independent of said mechanical stiffness andopposed in magnitude and direction to said signal force, to restore saidarmature to its null position.

2. An actuator which comprises an armature composed of magneticallypermeable material, a yieldable mounting -for said armature, permanentmagnet means positioned in operative relation adjacent said armature,means for mechanically applying a force to said armature in response toa signal, to move said armature from a null position, -the force ofmagnetic attraction of said permanent magnet means substantiallybalancing the mechanical stiffness of said yieldable mounting, and a jetpipe connected to said armature and movable in response to displacementof said armature, and means for applying to said armature a restoringforce independent of said mechanical stiffness and opposed in magnitudeand direction to said signal force, to restore said armature to its nullposition.

3. An actuator which comprises an armature composed of magneticallypermeable material, a yieldable mounting for said armature permanentmagnet means positioned in operative relation adjacent said armature,means 'for mechanically applying a -force to said armature, to move saidarmature from a null position, the force of magnetic attraction of saidpermanent magnet means substantially balancing the mechanical stiffnessof said yieldable mounting, a motion transmitting device connected tosaid armature and operative in response to motion of said armature,means movable responsive to the motion of said motion transmittingdevice, and a feedback means connected to said motion transmittingdevice and said last named movable means for restoring said armature toits null position.

4. An actuator which comprises an armature composed of magneticallypermeable material, a yieldable mounting for said armature permanentmagnet means positioned in operative relation adjacent said armature,means for mechanically applying a force to said armature, the force ofmagnetic attraction of said permanent magnetic means substantiallybalancing the mechanical stiffness of said yieldable mounting, a jetpipe connected to said armature and movable 4from a null position inresponse to displacement of said armature, means movable responsive tothe motion of said jet pipe and a feedback means connected to said jetpipe and said last named movable means for restoring said pipe to itsnull position.

5. An actuator which comprises an armature composed of magneticallypermeable material, a yieldable mounting for said armature permanentmagnet means positioned in operative relation adjacent said armature,means for mechanically applying a force to said armature, the force ofmagnetic attraction of said permanent magnet means substantiallybalancing the mechanical stitfness of said yieldable mounting, a jetpipe connected to said armature and movable from a null position inresponse to displacement of said armature, means movable responsive tothe deflection of a fluid stream from said jet pipe on motion thereof,and a feedback means connected to said jet pipe and said last namedmovable means for restoring said pipe to its null position.

6` An actuator which comprises an armature composed of magneticallypermeable material, a yieldable mounting for said armature, permanentmagnet means positioned in operative relation adjacent said armature,means for mechanically applying a force to said armature, the force ofmagnetic attraction of said permanent magnet means substantiallybalancing the mechanical stiffness of said yieldable mounting, a jetpipe connected to said armature and movable from a null position inresponse to displacement of said armature, means movable responsive tothe deflection of a uid stream from said jet pipe on `motion thereof,and a force feedback connected to said jet pipe and said last namedmovable means for restoring said pipe to its null position.

7. A11 actuator as defined in claim l, including means for adjustingsaid armature in said null position corresponding to a base signal forceapplied to said armature.

8. An actuator which comprises an armature support frame, an armature insaid frame, said armature composed of magnetically permeable material, ashaft tixedly con- 'assente nected to said armature and to said frame, atorsional flexure in said shaft, permitting said armature to moveangularly with respect to said shaft, a magnet vassembly mounted one ateach end of said armature frame, said assembly comprising a pair ofpermanent magnets and a pair of pole pieces, one of the pole pieces Vineach assembly being connected to a north magnetic pole of each of saidmagnets of said pair, and another of the pole pieces in each assemblybeing connected to a south magnetic `pole of each said magnet of saidpair, said pole pieces in each assembly being spaced to form a gap, oneend of said armature being positioned in one of said gaps, and the otherend of said armature being positioned in the other of said gaps, meansfor mechanically applying a force to said armature in response to asignal, to move said armature from a null position, the force ofmagnetic attraction of the pole pieces of said permanent magnets forsaid armature substantially balancing the mechanical stiffness of saidflexure, and a motion transmitting device associated with said armatureand operative in response to motion of said armature, and means forapplying to said armature a restoring force independent of saidmechanical stiffness and opposed in magnitude and direction to saidsignal force, to restore said armature to its null position.

9. An actuator which comprises a pair of spaced polarizing assemblies,each assembly composed of apair of permanent magnets, said magnets beingfastened at their north poles to a pole piece and at their south polesto a second pole piece, said pole pieces being spaced to for-m a gapcompleting a magnetic circuit through the pole pieces and each of saidpermanent magnets in each of said assemblies, an armature, said armaturecomposed of magnetically permeable material and extending into the gapin each of said `magnet assemblies, a mounting for said- Y armature,said mounting comprising a support, a flexure fixedly connected to saidarmature and said support for angular motion of said armature in saidgaps about an axis through said flexure, and mechanical means forapplying a force to said armature in response to a signal, to

move said armature from a null positio-n, the force of magneticattraction of the pole pieces of said permanent magnets for saidarmature substantially balancing the mechanical stiffness of saidfleXure, and -a jet pipe connected to said armature substantially atsaid axis and extendingmagnet assembly, an armature, said armaturecomposed f of magnetically permeable material and extending into thegaps between adjacent pole pieces of said magnetic assembly, a mountingfor said armature, said mounting comprising a support, a iiexure fixedlyconnected to said armature and said support for angular motion of saidarmature in said gaps about an axis'tthrough said flexure, a firstmechanical force transmitting means connected to said armature on oneside of said fiexure, a second mechanical force transmitting meansconnected to said armature on 'said one side of said flexure and inopposing relation to said first force transmitting means, thedistance-between said flexure and said first means being somewhatgreater than the `distance between said flex-ure and said second means,at least oneof said-force transmitting means being operative in responselto a signal, the force of magnetic attracl i6 assembly, pole piecesconnected to said assembly, :said pole pieces being spaced to form a gapcompleting a niagnetic circuit through the pole pieces and saidpermanent magnet assembly, an armature, said armature composed ofmagnetically permeable material and extending into the gaps betweenadjacent pole pieces of said magnet assembly, a mounting for saidarmature, said mounting comprising a support, a flexure xedly connectedto said armature and said support for angular motion of said armature insaid gaps about an axis through saidiiexure, a first pressure responsiveforce transmitting member connected to said armature on one side of saidfiexure, a second pressure responsive force transmitting memberconnected to said armature on the other side of said fiexure, said firstand second members being mounted equidistant from said llexure and inforce opposing relation on one face of said armature, a third pressureresponsive force transmitting member connected to said armature on saidone side of said ilexure, and a fourth pressure responsive forcetransmitting member connected to said armature on said other side ofsaid flexure, said third and fourth members being mounted equidistantfrom said flexure and in force opposing relation on the other face ofsaid armature, the distance between said flexure and each of said firstand second members being slightly greater than the distance between saidflexure and each of said third and fourth members, means for applyingequal pressures to said first and third members in response to a signal,means. for applying equal pressures 'to said second and fourth members,the force of magnetic attraction of the pole pieces of said permanentmagnets for said armature substantially Vbalancing the mechanicalstiffness of said dexure, and a motion transmitting device associatedwith said armature and operative in response to motion of said armature.

12. An actuator as defined in claim l1, wherein said motion transmittingdevice includes a jet pipe connected to saidV armature substantially atthe axis of said flexu're and extending perpendicular to said axis,means for passing fluid through said jet, and means responsive tothemovement of fluid from said jet pipe.

13. An actuator which comprises a pair of spaced polarizing assemblies,each assembly composed of a pair of permanent magnets, said magnetsbeing fastened `at their north poles to a pole piece and at their southpoles to a second pole piece, said pole pieces being spaced Vto form agap completing a magnetic circuit through the pole pieces and each ofsaid permanent magnets in each of said assemblies, an armature, saidarmature composed of magnetically permeable material and extending intothe gap in each-of said magnet assemblies, a mounting for said armature,said mounting comprising a support fastened t-o each of said assemblies,a flexure fixedly connected to said armature and said support forangular motion of said armature in said gaps about an `axis through saidfiexure, a first pressure responsive force transmitting bellowsconnected to said armature on one side of said flexure, a secondpressure responsive force transmitting bellows connected to saidarmature on said one side of said flexure in opposing relation tosaidfirst bellows, the distance between said flexure and said rst bellowsbeing slightly greater than the distance between said flexure and saidsecond bellows, means for app-lying pressure to said first and secondbellows, in response to a signal, the force of magnetic attraction ofthe pole pieces of said permanent magnets for said armaturesubstantially balancing the mechanical stiffness of said ilexure, and amotion transmitting Idevice associated with said armature and operativein response to motion of said armature.

14. An actuator as defined in claim 13, wherein said motion transmittingdevice includes ajet pipe connected to said Varmature substantially atsaid aXis of said exure,

- and means responsive to the movement of fluid from said rjet pipe forapplying to said armature a restoring force independent of saidmechanical stiffness and opposed in 1 1 magnitude and direction to saidsignal force, to restore said armature to its null position.

15. An actuator as defined in claim 13, including adjustable springmeans connected to one end of said armature for adjusting the armaturein a centered position between said pole pieces corresponding to a basesignal force applied to said armature.

16. An actuator which comprises a permanent magnet assembly, pole piecesconnected to said assembly, said pole pieces being spaced to form a gapcompleting a magnetic circuit through the pole pieces and said permanentmagnet assembly, an armature, said armature composed of magneticallypermeable material and extending into the gaps between adjacent polepieces of said magnet assembly, a mounting for said armature, saidmounting comprising a support, a exure fixedly connected to saidarmature and said support for angular motion of said armature in saidgaps about an axis through said flexure, mechanical means for applying aforce to said armature in response to a signal, the force of magneticattraction of the pole pieces of said permanent magnets for saidarmature substantially balancing the mechanical stiffness of saidytiexure, a jet pipe connected to said armature substantially at saidaxis and extending perpendicular to said axis and rotatable with saidarmature, an ejector jet at the end of said jet pipe, a pair ofstationary receptor jets positioned adjacent said ejector jet and influid communication with said ejector jet, said ejector jet discharginga greater amount of fluid in one of said receptor jets than in the otheron displacement of said ejector jet away from a centered positionbetween said receptor jets, movable means responsive to the displacementof said ejector jet, and means connected to said movable means and saidejector jet for applying to said armature a restoring force independentof said mechanical stiffness and opposed in magnitude and direction tosaid signal force, to restore said armature to its null position.

17. An actuator which comprises a pair of spaced polarizing assemblies,each assembly composed of a pair of permanent magnets, said magnetsbeing fastened at their north poles to a pole piece and at their southpoles to a second pole piece, said pole pieces being spaced to form agap completing a magnetic circuit through the pole pieces and each ofsaid permanent magnets in each of said assemblies, an armature, saidarmature composed of magnetically permeable material and extending intothe gap in each of said magnet assemblies, a mounting for said armature,said mounting comprising a support, a iexure fixedly connected to saidarmature and said support for angular motion of said armature in saidgaps about an axis through said tlexure, mechanical means for applying aforce to said armature in response to a signal, the force of magneticattraction of the pole pieces of said permanent magnets for saidarmature substantially balancing the mechanical stiffness of said exure,a jet pipe connected to said armature substantially at said axis andextending perpendicular to said axis and rotatable with said armature,an ejector jet at the end of said jet pipe, a pair of stationaryreceptor jets positioned adjacent said ejector jet and in fluidcommunication with said ejector jet, said ejector jet discharging agreater amount of fluid in one of said receptor jets than in the otheron rotation of said ejector jet away from a centered position betweensaid receptor jets, a sleeve, a movable spool in said sleeve, closedfirst and second chambers in said sleeve at opposite ends of said spool,a first port in said sleeve communicating with said first chamber, asecond port in said sleeve communicating with said second chamber, afirst channel between one of said receptor jets and said first port, anda second channel between said other receptor jet and said second port,and feedback means connected between said spool and said jet pipe forrestoring said pipe to its centered position.

18. An actuator which comprises a pair of spaced polarizing assemblies,each assembly composed of a pair of permanent magnets, said magnetsbeing fastened at their north poles to a pole piece and at their southpoles to a second pole piece, said pole pieces being spaced to form agap completing a magnetic circuit through the pole pieces and each ofsaid permanent magnets in each of said assemblies, an armature, saidarmature composed of magnetically permeable material and extending intothe gap in each of said magnet assemblies, a mounting for said armature,said mounting comprising a support fastened to each of said assemblies,a exure xedly connected to said armature and said support for angularmotion of said armature in said gaps about an axis through said tlexure,a first pressure responsive force transmitting bellows connected to saidarmature on one side of said exure, a second pressure responsive forcetransmitting bellows connected to said armature on the other side ofsaid exure, said first and second bellows being mounted equidistant fromsaid iiexure and in force opposing relation on one `face of saidarmature, a third pressure responsive force transmitting bellowsconnected to said armature on said one side of said flexure, and afourth pressure responsive force transmitting bellows connected to saidarmature on said other side of said tlexure, said third and fourthbellows being mounted equidistant from said flexure and in forceopposing relation on the other face of said armature, the distancebetween said flexure and the axis of each of said first and secondbellows being slightly greater than the distance between said flexureand the axis of each of said third and fourth bellows, means forapplying equal pressures to said first and third bellows, means forapplying equal pressures to said second and fourth bellows, the force ofmagnetic attraction of the pole pieces of said permanent magnets forsaid armature substantially balancing the mechanical stiffness of saidflexure, a jet pipe connected to said armature substantially at the axisof said exure and extending perpendicular to said axis and rotatablewith said armature, an ejector jet at the end of said jet pipe, a pairof stationary receptor jets positioned adjacent said ejector jet and influid communication with said ejector jet, said ejector jet discharginga greater amount of fluid in one of said receptor jets than in the otheron rotation of said ejector jet away from a centered position betweensaid receptor jets, a sleeve, a movable spool in said sleeve, closedfirst and second chambers in said sleeve at opposite ends of said spool,a first port in said sleeve communicating with said first chamber, asecond port in said sleeve communicating with said second chamber, afirst channel between one of said receptor jets and said first port, anda second channel between said other receptor jet and said second port,and a force feedback spring connected between said spool and said jetpipe.

19. An actuator which comprises a permanent magnet assembly having northand south poles located opposite each other, pole pieces mountedadjacent each other at said north and south poles, respectively, saidpole pieces being spaced to form a gap completing a magnetic circuitthrough the pole pieces and said permanent magnet assembly, an armature,said armature composed of magnetically permeable material and extendinginto 4the gaps between said adjacent pole pieces of said magnetassembly, a mounting for said armature, said mounting comprising asupport, a exure connected to said armature and said support for angularmotion of said armature in said gaps about an axis, said magnetic forcesubstantially balancing the stiffness of said exure, a mechanical forcetransmitting means connected to said armature operative in response to asignal, and a motion transmitting device associated with said armatureand operative in response to motion of said armature.

No references cited.

